The invention relates to automotive structural parts such as suspension arms, pivots and other similar parts.
The invention also relates to the technical field of casting or forging materials into light alloys of aluminium and similar types as well as to the technical sector combining operations of casting and forging.
The invention more specifically relates to the manufacture of automotive structural parts that meet highly particular specifications with regard to the functionality of the said structural parts considered. These are in fact subject to very strict technical and environmental stresses and constraints in respect of their applications in the fields of motor vehicles, heavy vehicles and other similar vehicles. The specifications are intended for example for resistance to stresses caused by endurance, crashes, buckling and quality requirement levels of welds. The stresses of these structural parts, in the particular case of vehicles, are also accentuated by soil conditions, vehicle rolling, speed thereof with an increase in vibrations. In case of a vehicle crash, these parts are often very easily damaged by inertia effects encountered with deformations or simply, cracks.
To meet these specifications, manufacturers, mainly companies specialising in casting and/or forging, will search for specific forms of these structural parts that are highly resistant to shocks and more generally loads. Thus, and in well-known manner, the structural parts have a cross section determined as ‘H’ the generator of which follows a direction perpendicular to the direction(s) of the stresses.
We have thus shown in FIGS. 1 and 2 an example of a structural part of the suspension arm type which according to the prior art has an ‘H’ section.
We have thus shown part (1) on the front side and back side with the arrow (F1) illustrating the direction of the highest stresses.
It should be noted that this said part (1) is obtained either, by a single casting and/or forging process with the acquisition of the final desired shape directly, or by the implementation of a process referred to by the trademark COBPRESS combining two successive operations of casting followed by forging. This was described in the EP 119365 patent developed and operated by the Applicant since 1983.
The configuration of part (1) thus helps to define stiffening edges (1a) that are more or less high depending on the applications. Cavities (1b) that have no specific function are thus formed on either side of the longitudinal median plane of part (1). The ends (1c) (1d) of the part are arranged in a known and variable manner with the sleeves or fastening rings, and with fastening parts.
The optimisation of these geometries in section ‘H’ helps to provide parts with better mass/performance ratio. In addition we know, according to basic concepts of solid mechanics that at equal mass, a tube provides more stiffness than a rod of complete cross-section.
The search for manufacturers of this type of structural parts is thus to design structural parts having hollow sections or areas for which the inertias are remote from the neutral axis in order to optimise the quadratic time, an improvement in the performance as regards resistance to stresses while minimising the mass of the part as much as possible.
This search for optimisation of the forms of the structural part must however take into account the above-mentioned technical and environmental stresses and constraints by ensuring excellent rigidity of the part while reducing its mass. In other words, the problem was to meet the paradoxical and contradictory requirements of lightness and rigidity of the part, without adding material.
The solution provided by the Applicant fully meets the above requirements, both in the context of the structural parts obtained by casting, and a joint process of casting and forging known under the trademark COBAPRESS and the object of the patent EP 119365.
From the patent KR 2012 0030852, we also know the manufacturing of suspension parts for motor vehicles that are present on the outer surface of a solid body of related exposed stiffening parts in order to limit or eliminate the effects of ruptures with regard to the end fastening portions of the suspension part.
From the patent DE 10217209, we know the creation of the arm from light alloy arm for a wheel suspension of the motor vehicle. In practice, according to this document the arm consists of the addition of two parallel plates which are fixed on the end parts (5 and 11) by defining a hollow interior volume. The manufacture of such an assembly is complex with many operations to ensure the connection between the parts.
Furthermore, this document describes parts in complex forms and with reduced sections that cannot be easily obtained by a casting process using light cast-iron alloys with high mechanical properties.
None of these documents implement the manufacture of a single piece obtained by a process of forging or casting.